Add XCUI editor collection primitives and stack rollback

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -31,13 +31,14 @@ Old `editor` replacement is explicitly out of scope for this phase.
 - Shared engine-side `UIDocumentScreenHost` now compiles `.xcui` / `.xctheme` screen documents into a runtime-facing document host path instead of leaving all document ownership in `new_editor`.
 - Shared text-editing primitives now live under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so UTF-8 caret movement, line splitting, and multiline navigation are no longer trapped inside `XCUI Demo`.
 - Shared text-input controller/state now also lives under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so character insertion, backspace/delete, submit, and multiline key handling no longer need to be reimplemented per host.
+- Shared editor collection primitive classification and metric helpers now also live under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets`, covering the current `ScrollView` / `TreeView` / `ListView` / `PropertySection` / `FieldRow` prototype taxonomy.
 - Core regression coverage now includes `UIContext`, layout, style, runtime screen player/system, and real document-host tests through `core_ui_tests`.
 
 Current gap:
 
 - Minimal schema self-definition support is landed, including consistency checks for enum/document-only schema metadata, but schema-driven validation for `.xcui` / `.xctheme` instances is still not implemented.
 - Shared widget/runtime instantiation is still thin and mostly editor-side.
-- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, tree/list virtualization, property-grid composition, and native image/source-rect level APIs.
+- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, real tree/list/property widget state on top of the new editor-primitive helpers, and native image/source-rect level APIs.
 
 ### 2. Runtime/Game Layer
 
@@ -45,6 +46,7 @@ Current gap:
 - The demo runtime has moved past single-line input: multiline `TextArea` behavior is now covered in the sandbox testbed.
 - Engine-side runtime ownership is no longer zero: `UIScreenPlayer`, `UIDocumentScreenHost`, and `UISystem` now define a shared runtime contract for loading a screen document, ticking it with input, and collecting `UI::UIDrawData`.
 - `UISystem` now supports layered screen composition semantics: stacked screen players, top-interactive input routing, and modal layers that block lower screens.
+- `UIScreenStackController::ReplaceTop` now preserves the previous top screen if the replacement screen fails to load, so runtime menu flows do not silently drop their active layer on bad assets.
 - Runtime screen emission now also carries concrete button text in the shared document host path instead of silently dropping button labels.
 
 Current gap:
@@ -82,7 +84,7 @@ Current gap:
 - `new_editor_xcui_rhi_render_backend_tests`: `5/5`
 - `new_editor_xcui_hosted_preview_presenter_tests`: `12/12`
 - `XCNewEditor` Debug target builds successfully
-- `core_ui_tests`: `26/26`
+- `core_ui_tests`: `28/28`
 - `core_ui_style_tests`: `5/5`
 - `ui_resource_tests`: `11/11`
 - `editor_tests` targeted bridge smoke: `3/3`
@@ -93,6 +95,7 @@ Current gap:
 - Demo runtime multiline `TextArea` path in the sandbox and test coverage for caret movement / multiline input.
 - Common-core `UITextEditing` extraction now owns UTF-8 offset stepping, codepoint counting, line splitting, and vertical caret motion with dedicated `core_ui_tests` coverage.
 - Common-core `UITextInputController` extraction now owns per-field text state, character insertion, enter-submit, and multiline keyboard editing behavior with dedicated `core_ui_tests` coverage.
+- Common-core `UIEditorCollectionPrimitives` extraction now owns the editor collection tag taxonomy and default metric resolution used by current `LayoutLab` widget prototypes, with dedicated `core_ui_tests` coverage.
 - Demo runtime text editing was extended with:
   - click-to-place caret
   - `Delete` support
@@ -117,6 +120,7 @@ Current gap:
   - `UISystem`
   - layered screen composition and modal blocking semantics
 - Runtime/game integration scaffolding now includes reusable `HUD/menu/modal` stack helpers on top of `UISystem`.
+- `UIScreenStackController` replacement now rolls back safely on failure instead of popping the active top layer first.
 - Runtime document-host draw emission now preserves button labels for shared screen rendering.
 - RHI image path improvements:
   - clipped image UV adjustment